Lightweight, high-strength pipes and profiles of circular or noncircular contours have hitherto been required in the diverse fields as mentioned above. For these applications fiber-reinforced composite resin pultrusion products in the form of pipes and profiles, especially of noncircular cross-sectional contours, are attracting increasing attention.
Conventionally, the fiber-reinforced composite resin pultrusion products are made by pulling axially arranged rovings of resin-impregnated reinforcing fibers through a die to a desired shape and then curing the shape. Such fiber-reinforced composite resin pultrusion products attain axial tensile and compressive strengths but are questionable in lateral strengths, e.g., in torsional and bending strengths. To clear up the question, the so-called overwinding method has been proposed which involves helically winding reinforcing fibers round a mandrel and subsequent forming of the fibers by a die into a desired shape and curing to a final pultrusion product. The products manufactured by overwinding exhibit increased lateral strengths but are yet to be improved in axial strengths.
Heretofore, when a fiber-reinforced composite resin pultrusion product of a noncircular cross-sectional contour, such as a hollow square article, is to be obtained, it has been necessary first to form an article of a circular cross section by pultrusion and then work it to change the contour from a circle to a rectangle. The fabrication involves extreme difficulties, and the fiber density is lessened at corners than in the rest, leading to ununiform fiber distribution in the matrix. These and other problems have rendered it difficult to obtain products of good qualities. Moreover, it has been impossible to manufacture fiber-reinforced composite resin pultrusion products of noncircular cross-sectional contours, e.g., of the letter L-, H-, and I-shape by the overwinding method as described above.
Japanese Patent Application Public Disclosure No. 62-90234 discloses fiber-reinforced composite resin products having circular and noncircular cross-sectional contours, each product comprising rovings arranged in a predetermined size and shape along the length of the product, normal cloths having warp and weft, bias cloths formed over the normal cloths at the portions on which shearing forces may be imposed, and a continuous strand mat covering the outer periphery of the product.
Such fiber-reinforced composite resin products exhibit increased axial strengths and shearing strengths to bending but are questionable in lateral strengths because the reinforcing fibers which are wound at 90.degree. and a certain angle with respect to the longitudinal axis of the product, each are discontinuous.
Further, the fiber-reinforced composite resin products require to cut the normal cloths, bias cloths and continuous strand mats in predetermined sizes and shapes prior to pultrusion. Furthermore, it is extremely difficult to arrange the web members in a given positional relationship along the rovings positioned in a predetermined shape and size, and to continuously draw the web members into a die to give the web laminate desired size and shape.
The present inventors, with the view to overcoming these difficulties of the prior art, have made extensive studies and experiments. It has now been found, as a result, that the combination of an axially-oriented fiber layer, formed of reinforcing fibers arranged axially, with a helical fiber layer, formed of reinforcing fibers wound helically with respect to the axis, imparts greater axial and lateral strengths to the product than does either layer alone.
Further studies and experiments by the present inventors on the manufacture of such fiber-reinforced composite resin pultrusion products by the overwinding technique, using carbon fiber in particular as the reinforcing fiber, revealed another problem. Especially in the process step of drawing an uncured carbon fiber-reinforced resin layer laminate consisting of axially-oriented and helical carbon fiber-reinforced resin layers into a die to give it desired size and shape, relative motion of the axially-oriented and helical carbon fiber-reinforced resin layers hampers the insertion of the helical carbon fibers at regular intervals. This was found to make it difficult to form a carbon fiber-reinforced resin layer laminate of a desired thickness and configuration.
In order to solve this problem, the present inventors have concentrated their efforts on the research and experiment on the structure and manufacture of carbon fiber-reinforced composite resin pultrusion products. It has now been found, as a result, that the above problem is solved by allowing either the axially-oriented carbon fiber-reinforced resin layer or the helical carbon fiber-reinforced resin layer or both to contain a given proportion of a fiber dissimilar to the carbon fiber, especially a dissimilar fiber in a fluffed state (in the form of woollike rovings of monofilaments in random orientation). It has also been found that the axial and lateral strengths of the pultrusion products thus obtained remain practically unchanged. This is presumably attributable to the fact the inclusion of a dissimilar fiber into a carbon fiber layer increases the frictional resistance of the layer sufficiently to hinder the relative motion of the layer and the overlying or underlying layer, thus preventing any irregular motion of the uncured carbon fiber-reinforced resin layer laminate while being drawn into the die.
The present invention is predicated upon this new discovery.
It is an object of the invention to provide fiber-reinforced composite resin pultrusion products having circular and noncircular cross-sectional contours markedly improved in axial and lateral strengths over conventional products.
Another object of the invention is to provide a method of manufacturing fiber-reinforced composite resin pultrusion products of not merely circular cross-sectional contours but also noncircular cross-sectional contours in particular, in a most simplified way and continuously by taking advantage of the over-winding technique.